Coupled cavity-type slow-wave structure

ABSTRACT

A slow-wave structure for a travelling-wave tube, comprising a tubular waveguide member, a plurality of electric conductive plates transversely affixed to the member and coaxially disposed in mutually spaced relation on a longitudinal axis of the member in a manner perpendicular thereto, the respective plates having aligned apertures for passing an electron beam therethrough and for propagating high-frequency energy in a state of electromagnetic interaction with the electron beam, and an attenuation section disposed substantially in the middle of the member and including two vessels disposed coaxially with the member longitudinal axis at juxtaposed ends of input and output sides of the member, at least a part of each of the vessels being made of high-frequency energy-permeable material, and water substantially filling the respective two vessels, whereby the high-frequency energy is attenuated in the respective vessels while the water therein serves as a coolant therefor.

United States Patent Horigome [4 1 Jan. 18, 197 2 s4] COUPLED CAVITY-TYPE SLOW-WAVE 3,221,204 11/1965 Hant et a1. ....31s/3.5 STRUCTURE 2,398,606 4/1946 Wang ..333/22 2,400,777 5/1946 Okress ..333/22 [72] Inventor: Toshinori Horigome, Tokyo, Japan [73] Assignee: Nippon Electric Company, Limited, f' "f Kafl saalbach Minatmku Tokyo Japan Assistant ExammerSaxfield Chatmon, Jr.

Attorney-Mam and Jangarathis [22] Filed: Aug. 21, 1970 [21] App]. No.: 66,041 [57] ABSTRACT A slow-wave structure for a travelling-wave tube, comprising a tubular waveguide member, a plurality of electric conductive {30] Foreign Application Priority Data plates transversely aff xed to the member and coaxially Aug. 30, 1969 Japan ..44/68987 disposed in mutually Spaced relation on a longiiudinal axis of the member in a manner perpendicular thereto, the respective s2 u.s. c1. ..3l5/3.6, 333/81, 333 31 A, plates having aligned apertures for Passing an electron beam 313 7 therethrough and for propagating high-frequency energy in a 51 Int. Cl. ..l-l01j 25 34 State of electromagnetic interaction with the electron beam, I 58] Field of Search "315/35, 333/22, 81, 81 C, and an attenuation section disposed substantially in the middle 333/31 A; 313/17 18 of the member and including two vessels disposed coaxially with the member longitudinal axis at juxtaposed ends of input 56] References Cited and output sides of the member, at least a part of each of the vessels being made of high-frequency energy-permeable UNITED STATES PATENTS material, and water substantially filling the respective two vessels, whereby the high-frequency energy is attenuated in the 2,939,993 6/1960 Zublm et a1 ..315/3.5 respective vessels while the water therein Serves as a coolant 3,360,750 12/1967 Johnson..... therefon 3,181,023 4/1965 l-lant et a1. ..3l5/3.5 3,123,736 3/1964 Christoffers et a1. ..3 l5/3.6 6 Claims, 3 Drawing Figures PATENTED JAM a rare f(GHZ) INVENTOR.

Toshinori Horigome ATTORNEYS COUPLED CAVITY-TYPE SLOW-WAVE STRUCTURE This invention relates to a coupled cavity-type slow-wave structure for a travelling-wave tube and the like and, more particularly, to an improved attenuator used for such slowwave structure.

The slow-wave structure of travelling-wave tube has an attenuator in order to prevent the tube from causing undesirable oscillation and to stabilize its amplifying operation. The attenuator which has hitherto been used for the coupled cavitytype slow-wave structure is made of a film having a large specific resistance. Such film is usually formed by spray on the inner wall of the cavity, or of a porous ceramic impregnated with carbon and inserted in the cavity. However, these conventional attenuators have shortcomings. For example, the attenuator of the former type using high-resistance film, when installed in only one cavity, does not exert sufiicient attenuation. Even when installed in more than one of the cavities, the output of the travelling-wave tube is reduced while the sufficient attenuation is obtained. The attenuator of the latter type using impregnated ceramic is capable of exerting sufficient attenuation, but is not suited for high-power operation. Therefore, when this type of attenuator is used for high-power travelling-wave tubes, the microwave causes temperature rise in the attenuator, releasing gas contained in the attenuator material, reducing the degree of vacuum of the tube and shortening the life of the tube.

An object of this invention is to provide a coupled cavitytype slow-wave structure having such attenuator as exerts sufficient attenuation with a minimum number of attenuators, without causing gas release even under high-power operation.

The coupled cavity-type slow-wave structure according to this invention comprises a plurality of cavities serially aligned along the axial line thereof, and an attenuator composed of liquid material disposed in at least one of these cavities. More specifically, the coupled cavity-type slow-wave structure of this invention is such that at least two partial cavities are disposed in alignment with each other. Each of the partial cavities consists of a plurality of serially aligned cylindrical cavities. An attenuator cavity, composed essentially of fluid material such as water, is disposed in between the partial cavities to couple them. The attenuator cavity consists of a coaxial shell having an inner diameter larger than that of the partial cavities, and wave-permeable insulation plates for hermetically dividing the shell concentrically and cylindrically. The attenuator may be formed of liquid material, such as water, filled in the space between the shell and the dividing plate. The attenuator cavity may be composed of the cylindrical outer shell, at least two wave-permeable insulation plates disposed in perpendicular relation to the axis of the shell for hermetically dividing the inside of the shell into several parts, and a drift tube disposed along the axes of the cavity and the plates for allowing electrons to travel therethrough. The fluid attenuation-exerting material fills the space defined by the shell, plates, and the drift tube. Specific heat of the liquid material used for the attenuator should be as large as possible. Neither dielectric constant nor electric conductivity of the material affects the electrical characteristics of the slow-wave structure.

In the coupled cavity-type slow-wave structure of this invention, liquid material, such as water used as attenuation-exerting element. It has been found that the attenuation exerted is sufficiently high, and is capable of withstanding high power, without causing any gas release.

The invention will be explained in detail by referring to the appended drawings, wherein:

FIG. 1 shows a longitudinal sectional view of a first embodiment of this invention;

FIG. 2 shows a family of curves illustrating the companion of the matching characteristic of the coupled cavity-type slowwave structure of this invention and that of the prior art; and

FIG. 3 is a longitudinal sectional view of a second embodiment of this invention.

Referring to FIG. I, the first embodiment of the invention comprises: an input terminating partial slow-wave circuit 7 consisting of a plurality of serially disposed cylindrical cavities 5. Each of the cavities 5 is defined by disc-shaped partition plates 3 each having a center aperture 1 for allowing an electron beam to pass therethrough and a coupling slot 2 for providing the electromagnetic coupling between the cavities. The plates 3 are disposed inside a cylindrical waveguide 4 at a predetermined interval. An output tenninating partial slowwave circuit 7 of similar the same composition as the circuit 7 is disposed in coaxial relationship-therewith. The partial slowwave circuits 7 and 7 are coupled with each other by attenuator cavities 8 and 8'. The inner diameter of these attenuator cavities 8 and 8 is larger than that of the cavity 5. Attenuators 9 and 9, formed of liquid material, such as water are disposed inside the attenuator cavities 8 and 8'. A partition plate 6 is disposed between cavities 8 and 8'. Also, an electromagnetic wave-permeable insulating cylindrical partition means 10 and 10' made of such material as ceramic are disposed inside the cavities 8 and 8, respectively. The liquid material 9 and 9' to serving as the attenuators fills the spaces outside the partition means 10 and 10'.

In the above arrangement, a high-frequency input signal is amplified in the input section 7 through interaction with the electron beam, and the amplified signal is terminated at the liquid material 9 contained in the cavity 8 which serves as a terminal cavity. The electron beam modulated by the said high-frequency input signal induces a high-frequency output signal in the output terminating partial slow-wave circuit 7. The reflected power of this high-frequency output signal is terminated at the liquid material load 9' contained in the cavity 8' which serves as a terminal cavity.

In the slow-wave circuit of this invention, sufficient attenuation can be effected by small number of attenuators, because said attenuators 9 and 9 are generally formed of water. In addition, because the power absorbed by water is converted into heat, the power capacity of the attenuator can be increased by causing flow in water. Furthermore, since the partition means 10 and 10' are made of ceramic or the like, there is no possibility of gas release.

Another feature of the first embodiment is that the matching between the attenuator elements 9 and 9 and the partial slow-wave circuits 7 and 7' can easily be adjusted by changing the inner diameter and thickness of each of the cavities 8 and 8' and the size of the coupling slot 2'.

Referring to FIG. 2, the matching characteristic of the slowwave structure of this invention is shown in comparison with that of the prior art 'using the attenuator of carbon-impregnated porous ceramic. The abscissa represents frequency f, and the ordinate indicates voltage reflection coefiicient or voltage standing wave ratio VSWR. As is apparently seen from the drawing, the matching characteristic curve 12 of the first embodiment is not worse than the curve 11 of the conventional slow-wave structure.

Referring to FIG. 3, the second embodiment of the invention is provided with cylindrical attenuator cavities 18 and 18' disposed in the portion in which the partial slow-wave circuit 7 is coupled with the output partial circuit 7', both similar to those of the first embodiment. Attenuator elements 19 and 19' made of water are disposed inside the cavities 18 and 18. A partition means 6 having in its center a drift tube for allowing the electron beam to travel therethrough is disposed between the cavities l8 and 18. Also, electromagnetic wave-permeable insulating partition means 20 and 20' are disposed at the respective ends of the drift tube. The attenuator elements 19 and 19 till the spaces surrounded by the partition plates 20 and 20', partition means 6 and waveguide 4. In this embodiment, the partition plates 20 and 20' may be disposed closer to the partition plate 6, and not at both ends of the drift tube.

In the second arrangement, as in the first embodiment, a high-frequency input signal is absorbed by the attenuation element 19, made of water. Also, the high-frequency signal reflected from the output end is absorbed by the water load 19'. Thus, sufficient attenuation can be realized by virtue of the attenuation elements 19 and 19. Power capacity of the attenuator can be increased by increasing the flow of water. In addition, there is no possibility of causing gas release from the attenuator.

Furthermore, the matching between the attenuators l9 and 19' and the slow-wave circuits 7 and 7' can be adjusted by changing the diameters of the cavities l8 and 18', distances from the partition plates 20 and 20' to the partition walls 3' and 3" of the cavity immediately adjacent to these partition walls, and sizes of the coupling slots 2' and 2" of the partition walls3' and 3".

As is shown in FIG. 2, the matching characteristic curve 21 of the second embodiment is not worse than that of the conventional slow-wave structure.

While a few specific embodiments of the invention have been described in detail, it should particularly be understood that the invention is not limited thereto or thereby.

What is claimed is:

l. A slow-wave structure for a travelling-wave tube, comprising:

a tubular conductive waveguide member;

a plurality of electric conductive plates transversely affixed in parallel spaced relation internally of said member to extend perpendicular to a longitudinal axis thereof; said plates having central apertures aligned in the direction of said axis for permitting an electron beam to pass therethrough and for propagating high-frequency energy in a state of electromagnetic interaction with said electron beam; and

an attenuation section disposed substantially at the middle of said member; said section comprising at least one vessel disposed coaxially with said longitudinal axis; at least a part of said vessel being made of high-frequency energypermeable material; and

a liquid substance substantially filling said vessel, whereby said high-frequency energy is attenuated in said one vessel while said substance therein serves as a coolant therefor.

2. The slow-wave structure according to claim I wherein said attenuation section comprises a second vessel disposed coaxially with said longitudinal axis in juxtaposition with said one vessel at respective input and output sides of said member; at least a part of said second vessel being made of high-frequency energy-permeable material; and an additional portion of said substance substantially filling said second vessel, whereby said high-frequency energy is also attenuated in said second vessel while said additional substance serves therein as a coolant therefor.

3. The slow-wave structure according to claim 2 wherein said one vessel and said second vessel are annular in shape.

4. The slow-wave structure according to claim 2 wherein said input and output sides have a common internal diameter while said one vessel and said second vessel have a common internal diameter which is larger than said first-mentioned common internal diameter.

5. A slow-wave structure according to claim 2 wherein said input and output sides, said one vessel and said second vessel have a common internal diameter.

6. A slow-wave structure according to claim 2 in which said first-mentioned substance and said additional substance portion comprise substantially water. 

1. A slow-wave structure for a travelling-wave tube, comprising: a tubular conductive waveguide member; a plurality of electric conductive plates transversely affixed in parallel spaced relation internally of said member to extend perpendicular to a longitudinal axis thereof; said plates having central apertures aligned in the direction of said axis for permitting an electron beam to pass therethrough and for propagating high-frequency energy in a state of electromagnetic interaction with said electron beam; and an attenuation section disposed substantially at the middle of said membEr; said section comprising at least one vessel disposed coaxially with said longitudinal axis; at least a part of said vessel being made of high-frequency energy-permeable material; and a liquid substance substantially filling said vessel, whereby said high-frequency energy is attenuated in said one vessel while said substance therein serves as a coolant therefor.
 2. The slow-wave structure according to claim 1 wherein said attenuation section comprises a second vessel disposed coaxially with said longitudinal axis in juxtaposition with said one vessel at respective input and output sides of said member; at least a part of said second vessel being made of high-frequency energy-permeable material; and an additional portion of said substance substantially filling said second vessel, whereby said high-frequency energy is also attenuated in said second vessel while said additional substance serves therein as a coolant therefor.
 3. The slow-wave structure according to claim 2 wherein said one vessel and said second vessel are annular in shape.
 4. The slow-wave structure according to claim 2 wherein said input and output sides have a common internal diameter while said one vessel and said second vessel have a common internal diameter which is larger than said first-mentioned common internal diameter.
 5. A slow-wave structure according to claim 2 wherein said input and output sides, said one vessel and said second vessel have a common internal diameter.
 6. A slow-wave structure according to claim 2 in which said first-mentioned substance and said additional substance portion comprise substantially water. 